Adnams, the Suffolk brewer that won the first "small company of the year award" from Business in the Community in 2003, has quit the campaign group, saying it is too soft on members who behave irresponsibly.

Simon Loftus, Adnams' chairman, told the Financial Times he was concerned that some companies used membership of the 700-member BITC as "a PR figleaf".

Given public mistrust of business, he said the organisation should publicly challenge poorly performing members to improve, rather than relying on behind-the-scenes persuasion.

The last straw for Mr Loftus appears to have been last month's re-election as a BITC director of Sir Peter Davis, former chief executive and chairman of J Sainsbury. Shareholders fumed last year when Sir Peter, a former chairman of BITC, was ousted from Sainsbury with a £2.6m bonus after failing to improve its fortunes.

"What does it say about an organisation like BITC if . . . one of its directors has been characterised by the press as being an exemplar of what people don't like about directors?" Mr Loftus said yesterday. "It tends to undermine credibility."

Adnams, resigned its membership after last month's annual general meeting.

Gail Greengross, head of communications strategy for BITC, said it was saddened by Adnams' resignation as Mr Loftus was "a very powerful force for change".

But she said BITC's corporate responsibility index was a way of publicly challenging companies to improve. Participation in the index was voluntary but there was peer pressure to join, said Ms Greengross. "We hope that it's harder and harder to come into BITC and not do anything."

She said Sir Peter was re-elected in recognition of his long-standing work for the campaign and that no other members voted against.